1. Field of the Invention
The present invention relates to a method and device for localizing an acoustic image at an arbitrary position when audio signal outputted from an audio appliance is heard via a headphone.
2. Description of the Related Art
Conventionally, various methods for localizing an acoustic image out of the head of a listener when a reproduced sound about music or the like is heard via a headphone have been proposed.
When a reproduced sound of music or the like is heard via a well known headphone, an acoustic image exists in the head of a listener so that audibility of this case is quite different from when a music or the like is heard via speakers placed in an actual sound space driven. Therefore, various technologies and researches for localizing an acoustic image out of the head of the listener when listening via a headphone, so as to obtain a similar audibility to when a sound is reproduced via external speakers have been proposed.
However, up to now proposed methods for localizing an acoustic image out of the head have not succeeded in obtaining sufficiently satisfactory acoustic image out of the head.
Accordingly, the present invention has been achieved in views of the above-mentioned problem and therefore, it is an object of the invention to provide a method for localizing an acoustic image out of the head upon listening via a headphone capable of obtaining an audibility just as if a reproduced sound is heard at a listening point via actual speakers, different from conventional methods and a device for achieving the same method.
To achieve the above object, according to an aspect of the present invention, there is provided a method for localization of an acoustic image out of the head in hearing a reproduced sound via a headphone, comprising the steps of: with audio signals of left, right channels reproduced by an appropriate audio appliance as input signals, branching the input signals of the left and right channels to at least two systems; to form signals of each system corresponding to the left, right channels with left, right speaker sounds imagined in an appropriate sound space with respect to the head of a listener wearing a headphone and virtual reflected sound in the virtual sound space caused from a sound generated from the left and right virtual speakers, creating a virtual speaker sound signal by processing so that the virtual speaker sounds from the left and right speakers are expressed by direct sound signals, and virtual reflected sound signals by processing so that the virtual reflected sound is expressed by reflected sound signal; mixing the direct sound signal and reflected sound signal of each of the left, right channels created in the above manner with mixers for the left and right channels; and supplying both the speakers for the left, right ears of the headphone with outputs of the left and right mixers.
According to the method of the present invention having such a configuration, each of the sound signals of the left, right virtual speakers and virtual reflected sound is divided to at least two frequency bands. Then, the virtual speaker sounds and virtual reflected sound appealing to man""s sense of hearing are formed by processing the divided signal of each band by controlling a feeling of sound direction and a feeling of a distance up to the virtual speaker and reflection sound source. These signals are mixed in the left, right mixers and the left, right mixers are connected to the left, right speakers.
In the present invention, a factor for the feeling of the directions of the virtual speaker and virtual reflection sound source depends on a difference of times of acoustic frequencies entering into the left and right ears of a listener or a difference of volume or differences of time and volume. Further, a factor for the feeling of the distance up to the virtual speakers and virtual reflection sound source depends on a difference of volume of acoustic frequency signals entering into the left and right ears or a difference of time or differences of volume and time.
Therefore, according to another aspect of the present invention there is provided a method for localization of an acoustic image out of the head in hearing a reproduced sound via a headphone by processing audio signals for the left, right speakers of the headphone, comprising the steps of: dividing the audio signal to audio signal for virtual speaker sound and audio signal for virtual reflected sound so as to form left, right virtual speaker sounds and virtual reflected sound of the virtual speaker sound from audio signal reproduced by an appropriate audio appliance; dividing each of the audio signals to low/medium range and high range or low range and medium/high range or low range and medium/high range in terms of frequency band; for the medium range, making a control based on a simulation by head transmission function of frequency characteristic; for the low range, making a control with a time difference or a time difference and a volume difference as parameter; and for the high range, making a control with a volume difference or a volume difference and a time difference by combfilter processing as parameter.
Further, according to still another aspect of the present invention, there is provided a device for localization of an acoustic image out of the head in hearing a reproduced sound via a head phone, comprising: a signal processing portion for left, right virtual speaker sounds for processing the virtual speaker sounds based on a function of transmission up to an entrance of the concha of a headphone user corresponding to the left, right speakers imagined in an any virtual sound space; a signal processing portion for the left, right reflected sounds based on the function of transmission of the virtual reflected sound because of a reflection characteristic set up arbitrarily in the virtual sound space; and left, right mixers for mixing processed signals in the signal processing portion in an arbitrary combination, speakers for the left, right ears of the headphone being driven by an output of the left, right mixers.